The major aims of this proposal are to identify signaling mechanisms initiated by FGFs that underlie normal development of the palate and the midface. Conditional deletion of the two receptors Fgfr1 and Fgfr2 lead to multiple craniofacial defects. Although FGF signaling has been extensively studied from a biochemical standpoint in many laboratories, including our own, remarkably little is known about how these signaling pathways regulate morphogenetic processes in craniofacial development. In this application, we propose: 1. To investigate the pathways regulated by FGF signaling in the palatal epithelium. Loss of Fgfr2 in the epithelium leads to a cleft palate. To establish the signaling mechanisms underlying this defect, we will generate and analyze an allelic series of conditional signaling mouse mutants at the Fgfr2 locus that prevent the binding of single or multiple effector proteins. We will further characterize transcriptional targets of Fgfr2 signaling in the palatal epithelium and determine if they can regulate subsequent proliferation of the underlying mesenchyme. 2. To investigate the pathways regulated by FGF signaling in the neural crest. Loss of Fgfr1 in the neural crest leads to multiple craniofacial defects, including in palate closure. To identify the underlying signaling mechanisms, we will generate and characterize an allelic series of conditional signaling mouse mutants at the Fgfr1 locus that prevent the binding of single or multiple effectors proteins, targeting the same pathways as for Fgfr2. Since the palate and other craniofacial organs are derived from neural crest cells migrated from dorsal neural ectoderm, we will also conduct Cre based lineage analysis to characterize defects in neural crest cell migration that underlie the mutant phenotypes. 3. To identify and characterize the FGF regulated pathways that control frontonasal development. Combined loss of both Fgfr1 and Fgfr2 in neural crest cells leads to facial clefting that extends through the midline. To establish the mechanistic basis for this phenotype, we will perform conditional mutagenesis in neural crest cells with compound Fgfr1 and Fgfr2 conditional mutants carrying point mutations for identical effectors, and compare these to the double null mutants. We will further establish the role of FGF signaling in midface development by conditional mutagenesis specifically in the frontonasal process. The proposed studies are anticipated to have a significant impact in craniofacial biology because they will establish the signaling mechanisms by which FGFs exert their action and open new directions for the prevention of craniofacial birth defects by the possible application of drug targets for critical FGF intracellular effectors.